If they are unused in the session_nonblock() function, there's a bigger
problem since then you won't get your socket non-blocking!

> - comparison between signed and unsigned integer expressions

I don't approve of those changes. Sockets in windows may be unsigned, but they
are then of type SOCKET and thus the reasonable change is to make sure we
detect the correct type and use that all over internally. I suggest we name it
libssh2_socket_t in a manner like: